Rectifier



Patented Jan. 18, .1949

RECTIFIER.

Charles 8. Duncan,

Wilkinsburg, Pa., assignor to Westinghouse Electric Corporation, EastPittsburgh, Pa.,

N Drawing. Application a corporation of Pennsylvania October 29, 1945,

Serial No. 625,452

4 Claims. 1

My invention relates to copper oxide rectifiers and inparticularly'relates to an improved type of copper oxide rectifier whichis subjected to a novel heat treating schedule.

One object of my invention is to provide a novel type of copper oxiderectifier.

Another object of my invention is to provide a novel process fortreating copper oxide units in the manufacture of devices exhibiting aunilateral conductivity.

Still another object of my invention is to provide a copper oxiderectifier in which the reverse current is lower than in copper oxiderectifiers of the prior art.

Still another object of my invention is to provide copper oxiderectifiers which can be operated at higher voltage per rectifier platethan copper oxide rectifiers of the prior art.

Still another object-of my invention is to provide a copper oxiderectifier capable of being operated at a greater power output for agiven efiectiveness of cooling them than can copper oxide rectifiers ofthe prior art.

Still another object of vide a copper oxide rectifier having a higheremciency of operation than copper oxide rectifiers of the prior art.

A still further object of my invention is to provide a copper oxiderectifier in which the electrical characteristics undergo less change orageing during operative life than copper oxide rectifiers of the priorart.

Other objects of my invention will become.

apparent upon reading the following description of the rectifier and theprocess of making it which embodies the principles of my invention.

As is well known in the art, dry contact rectifiers which have highlydesirable for many purposes can be made by forming on the surface ofcopper discs or plates, a thin layer of cuprous oxide; and providingsome form of conductive contact layer, such as Schoop-sprayed metaldeposited on a thin graphite layer covering the free surface of thecuprous oxide. In accordance with one widely used process of the priorart such rectifiers are first oxidized by heating the copper nearly to1,000 C. for 10 to 15 minutes, then annealing the units in air at around550 C. for a similar period and then quenching them in water. The layerof cupric oxide thus formed outside the cuprous oxide is then removed byetching in diluted sulphuric acid or the like. Rectifier elementsproduced by this general method have a maximum operating voltage of 3 to5 volts direct current output per unit when operating as characteristicsmy invention is to protion method described in a full wave bridgeconnection fed by a singlephase alternating current supply and 6 to 8volts direct current output per unit when operated similarly from athree-phase supply connection.

Substantial improvements over such rectifiers have been found possibleby employing the oxidaan application, Serial No. 509,819, filed November10, 1943, by Carl C. Hein, and entitled Rectifier elements, nowabandoned. Briefly, the Hein process comprises heating the copper blanksto around 955 C. in a furnace through which substantially pure carbondioxide is being passed for a preheating period of the order of 30minutes; then admitting oxygen for a period of from 4 to 6 minutes,after which purified carbon dioxide is again passed through the furnacewhile the temperature is lowered to about 550 C. After standing forabout 10 minutes at this temperature, the units are quenched in water atroom temperature. Such elements operate up to 20 volts direct currenteach on a full wave bridge connection fed by single-phase supply and 50volts direct current each on a similar connection fed by three-phasesupply.

Rectifiers made by the improved process I describe below can besuccessfully operated at directcurrent voltages as high as 50 volts perelement with a full wave bridge connection fed from a single phasesupply, and volts per element on a full wave three-phase bridge.

My improved rectifiers may be oxidized by following the above mentionedHein process through the 4 to 6 minute treatment in the atmospherecontaining oxygen. However I have found that by controlling the rate atwhich the units cool after such oxygen treatment through the 550 C.temperature and preferably continuing the slow temperature drop down toa temperature around 347 C., the entirecooling period consuming from 2to 4 hours, a great improvement in performance of the rectifiers evenover those made by the Hein process is attained. This cooling afteroxidation may be carried out in at atmosphere of carbon dioxide. Theshape of the cooling curve followed during the above mentioned 2 to 4hour drop is preferably one in which the temperature falls ratherrapidly at first and then slopes off gradually approaching the lowertemperature. While the precise shape of this curve may be varied in thecase of certain types of rectifiers, I have found that the followingschedule produces very satisfactory results in most cases and may betaken as typical. Starting at 955 C. at which oxidation has been carriedout, the temperature falls to 452 C. in approximately 21 minutes then 3to 400 C. in about 13 minutes; then to 347 C. in one hour and 40minutes; then remaining at 347 C. to make the total time elapsed duringcooling three hours. At the terminationoi' three hours, the units arequenched in water.

While I have described the application of my process to units oxidizedin accordance with the Hein process above-mentioned, it is within thepurview of my invention to employ it with rectifier discs oxidized byother methods known to the art.

To illustrate the improvement resulting from the above described heattreating process, im-

. pression of 15 volts per unit in the reverse direction passes onlyfrom 0.35 to 0.55 milliampere in the case of the above described unitswhereas the same voltage passes 0.7 to 1.1 milliamperes in the case ofthe units made by the Hein process above described; and the same voltagepasses to 10,

milliamperes in the caseof copper oxide rectifiers made by the prior artprocess described in the prior art process of this specification. Thisshows a reverse current under standard test conditions for my unit whichis only about & of that exhibited by conventional prior art units. Sincethe reverse current is a large factor in determining the amount of heatdispersed in dry contact rectifier units, and this heat dissipatedlargely controls the amount of voltage which the units can supply to adirect current load, it is obvious that my units represent a wideadvance over conventional prior art rectifiers.-

In accordance with another standard test frequently applied to drycontact rectifiers, these voltages required to pass /2 an ampere througha. disc 1 in outside diameter with a /2" hole in it, my units require1.2 to 1.9 volts; units made by the'Hein process above described require0.9 to 1.5 volts whereas conventional rectifiers made in accordance withthe first process described in this application require from .4 to 0.45volt. In view ofthe higher output voltage per unit than either the Heinor the first-described process units made by myprocess have a much lowerratio of internal voltage drop to output voltage, and so have a higherelectrical efiiciency, than rectifiers made by' *ither of the otherprocesses I have mentioned. Likewise I have found rectifier units madeby my process to undergo far less variation of electricalcharacteristics with operation than do other rectifiers.

I claim as my invention:

1. The method of heat treating oxidized copper units exhibitingunilateral conductivity which comprises reducing their temperature fromthat of oxidation to that at the end of the annealing during a period ofabout 3 hours; dropping to the neighborhood of 450 C. in a period in theorder of 21 minutes, then dropping to a temperature in the neighborhoodof 400 C. in a period in the order of 13 minutes, then dropping to about350 C. in about one hour and 40 minutes, and remaining at the lastmentioned temperature until the expiration of the three hour periodwhereupon the units are reduced rapidly to room temperature.

2. The method of manufacturing copper oxide rectifiers which comprisespreheating copper at a temperature near the melting point of copper fora period of the order of thirty minutes in substantially pure carbondioxide, maintaining the same temperature for a period of 4 to 6 minutesin an oxidizing atmosphere, thereafter cooling the units in anatmosphere of substantially pure carbon dioxide during an annealingperiod of from 2 to 4 hours, the temperature falling during thisannealing period first at a relatively rapid rate and thereafter at asubstantially slower rate, and then rapidly reducing the units to roomtemperaure.

3. The method of manufacturing copper oxide rectifiers which comprisespreheating copper at a temperature near the melting point of copper fora period of the order of thirty minutes in substantially pure carbondioxide, maintaining the same temperature for a period of 4 to 6 minutesin an oxidizing atmosphere, thereafter cooling the units in anatmosphere of substantially pure carbon dioxide during an annealingperiod of the order of 3 hours, the temperature falling during thisannealing period first at a relatively rapid rate and thereafter at asubstantially slower rate, and then rapidly reducing the units to roomtemperature.

4. The method of manufacturing copper oxide rectifiers which comprisespreheating copper at a temperature near the melting point of copper foraperiod of the order of thirty minutes in substantially pure carbondioxide, maintaining the same temperature for a period of'4 to 6 minutesin an oxidizing atmosphere, thereafter cooling the units in anatmosphere of substantially pure carbon dioxide during an annealingperiod of the order of 3 hours, the temperature falling to theneighborhood of 450 C. in a time of the order of 21 minutes, then to atemperature in the order of 400 C. during a period of 13 minutes, thenfalling to a temperature of the order of 350 C. in a-time of the orderof one hour and 40 minutes, and remaining at the last mentionedtemperature until the termination of the annealing period whereupon theunits are quickly reduced to room temperature.

CHARLES S. DUNCAN.

REFERENCES CITED 'The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

